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Study Examines Clinical Effects of Dichotomous 8-Minutes Response Times

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Review Of: Blanchard IE, Doig C, Hagel B, et al. Emergency medical services response time and mortality in an urban setting. Prehosp Emerg Care. 2012;16(1):142–151.

The Science
This is a retrospective study of a single EMS system from a large urban setting, examining the clinical effect of emergent response times of greater than 8:00 minutes and less than 7:59 minutes. Investigators defined response times as receipt of 9-1-1-call to on-scene time. More than 7,000 EMS responses were included in the analysis, examining several factors, including death. Results showed a 0.7% greater difference between patients who had a response time of less than 7:59 versus those with greater than 8:00 minutes Overall, the investigators concluded that there may be a small benefit to response times of less than 7:59, but failed to reach statistical significance.

Dr. Wesley: The debate over response time continues. These authors have provided us with an unprecedented view of a large urban system’s experience. Their data confirms conventional wisdom that most lives are saved within four to six minutes of 9-1-1 call receipt. What their data states is that those patients with life-threatening conditions have a 19% greater likelihood of dying if we take longer than eight minutes to respond.

But there are some nuances to this study that we should discuss. They define response time as being from the point when the 9-1-1 center answers the call until the arrival of the ambulance at the scene. Most American systems define response time as starting when 9-1-1 tones out the ambulance.

A quality dispatch center strives to dispatch Echo and Delta calls within 30–90 seconds of receipt. However, my experience is that the 9-1-1 call intake time averages 90–120 seconds for these calls. This would imply that American EMS should respond within six minutes of being toned out to achieve the same level of mortality as this Canadian service.

However, perhaps we do meet that level of performance. This study did not track the arrival time of BLS first responders. It has been shown that the arrival of first responders is more closely related to survival than the arrival time of the ambulance. In this study, BLS responded first 60% of the time, though they did not track their response time. Future studies should track both the response time of first responders as well as the ALS ambulance.

The decision to change system design to potentially capture those additional patients is a difficult one that must be weighed against the additional cost of such a program. At the end of the day, we must recognize that no system can ensure that all potential saves can be provided with a rapid response.

Medic Marshall: OK, let’s get something straight here. We’re still basing how we respond to emergent calls on a study that came out in early 80s that showed that there was improved survival from sudden cardiac arrest when patients were defibrillated in less than eight minutes. Does anyone else see a problem with this? It’s 30 years later. In my opinion, it’s time to start making some changes.

Don’t get me wrong, response times are an important factor in what we do, but it isn’t the end all-be all. Ultimately, research has yet to really find the magic mark on when responses times actually make a difference. The problem with this: If someone was complaining of chest pain for three days and finally decides to call 9-1-1, I’m almost certain that if you get there two minutes later than the eight-minute mark, it’s not going to make much difference; the damage has been done.

So what changes can we make? For starters, we need to start doing a better job at educating our public and elected officials on the importance of response times and outcomes or, in this case, unimportance. Furthermore, it doesn’t take a rocket scientist to tell you that reducing response times is expensive. Now there is something to evaluate: the cost of reducing response times incrementally and linking that to patient outcomes. Just in case someone is lying around looking for some research to do.

Abstract
Blanchard IE, Doig C, Hagel B, et al. Emergency medical services response time and mortality in an urban setting. Prehosp Emerg Care. 2012;16(1):142–151.

Background: A common tenet in emergency medical services (EMS) is that faster response equates to better patient outcome, translated by some EMS operations into a goal of a response time of eight minutes or less for ALS units responding to life-threatening events.

Objective: To explore whether an eight-minute EMS response time was associated with mortality.

Methods: This was a one-year retrospective cohort study of adults with a life-threatening event as assessed at the time of the 9-1-1 call (Medical Priority Dispatch System Echo- or Delta-level event). The study setting was an urban all-ALS EMS system serving a population of approximately 1 million. Response time was defined as 9-1-1 call receipt to ALS unit arrival on scene, and outcome was defined as all-cause mortality at hospital discharge. Potential covariates included patient acuity, age, gender, and combined scene and transport interval time. Stratified analysis and logistic regression were used to assess the response time–mortality association.

Results: There were 7,760 unit responses that met the inclusion criteria; 1,865 (24%) were ≥8 minutes. The average patient age was 56.7 years (standard deviation = 21.5). For patients with a response time ≥8 minutes, 7.1% died, compared with 6.4% for patients with a response time ≤7minutes 59 seconds (risk difference 0.7%; 95% confidence interval [CI]: –0.5%, 2.0%). The adjusted odds ratio of mortality for ≥8 minutes was 1.19 (95% CI: 0.97, 1.47). An exploratory analysis suggested there may be a small beneficial effect of response ≤7 minutes 59 seconds for those who survived to become an inpatient (adjusted odds ratio = 1.30; 95% CI: 1.00, 1.69).

Conclusions: These results call into question the clinical effectiveness of a dichotomous eight-minute ALS response time on decreasing mortality for the majority of adult patients identified as having a life-threatening event at the time of the 9-1-1 call. However, this study does not suggest that rapid EMS response is undesirable or unimportant for certain patients. This analysis highlights the need for further research on who may benefit from rapid EMS response, whether these individuals can be identified at the time of the 9-1-1 call, and what the optimum response time is.

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